A device of this type mentioned in the opening paragraph is described in U.S. Pat. No. 5,194,862. For the sensor device (realized on a panel) described in this patent, it is indicated how it can be used as an overlay for a liquid crystal display device (LCD).
When this type of device is used, notably in portable applications (mini-notebook computers, personal digital assistance devices, telecommunication), it is desirable that a minimal quantity of energy is used.
A further problem is that reflection occurs on reflective faces of the panel. This is at the expense of contrast and color purity.
It is, inter alia, an object of the present invention to provide a device of the type described in which one or more of the above-mentioned problems are largely prevented.
To this end, a device according to the invention is characterized in that the sensor device comprises at least one substrate, a main face of which extends at an angle a with respect to a main face of a substrate of the display device, in which 0&lt;.alpha.&lt;15 degrees.
By placing the substrate of the sensor device at an angle, incident light is reflected through such an angle that it usually does not reach the eye of an observer. The loss of contrast and color purity is thereby largely prevented. This is already achieved at an angle .alpha.&lt;5 degrees.
Usually, the substrates of the sensor device are parallel. The substrate remote from the display device is preferably placed at an angle a because the reflections on this surface are most disturbing.
A preferred embodiment of a device according to the invention is preferable characterized in that a substrate of a display device remote from the sensor device is provided with a reflector. The use of the reflector provides the possibility of refraining from a backlight, which has an energy-saving effect.
The reflector may be provided on the inner side or the outer side of the substrate of the display device.
In a further embodiment, the substrate of the display device remote from the optical guide comprises a silicon substrate in which, for example drive switches are realized (active addressing) or which incorporates further drive functions.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.